The invention relates to an electrode arrangement comprising an electrode line carrying at least a first fixing element which is designed to fix the electrode line to body tissue, in particular the myocardium of a heart, and which is arranged at a spacing relative to the distal end of the electrode line.
The invention further relates to an electrode line having electrodes for the stimulation of the myocardium of a human heart or for picking up electrical signals from a human heart. Electrode lines of that kind are used in particular in connection with an implanted cardiac pacemaker which provides artificial stimulation by way of the electrodes of the electrode line.
An aspect of particular interest is, inter alia, stimulation of the septum between the left and right ventricles of the heart. Electrode arrangements for septum stimulation are known for example from German application 195 46 941, and U.S. Pat. Nos. 5,728,140, 5,683,447, 5,476,500 and 5,693,081. None of those electrode lines satisfactorily permits bi-phase stimulation of the upper septum. Anchorage of the electrode line in the septum is also not satisfactorily achieved with the known electrode arrangements.
Having regard to the background of the state of the art, the object of the invention is to afford an alternative electrode arrangement which as far as possible avoids the described disadvantages of the state of the art.
In accordance with the invention, this object is attained by an electrode arrangement of the kind set forth in the opening part of this specification, in which the first fixing element is fixedly connected to the electrode line and has at least one free end extends tangentially outwardly from the electrode line and that is configured so that the first fixing element penetrates body tissue by a rotary movement of the electrode line about its longitudinal axis thereof.
An electrode arrangement of that kind advantageously manages without fixing means which are movable relative to the electrode line, as are known from U.S. Pat. Nos. 5,476,500, 5,683,447 and 5,693,081.
In one embodiment, the first fixing element is in the form of a helical coil that is rigidly connected to the electrode line so that the helical coil extends around the electrode line substantially coaxially at a spacing relative to the electrode line. The first fixing element is thus of a corkscrew-like configuration and is rigidly connected to the electrode line. By virtue of rotary movement of the electrode line about the longitudinal axis thereof, the free end of the fixing element hooks into adjacent body tissue and thus provides for secure fixing of the electrode line to the body tissue. That permits in particular active fixing to the septum of a heart. In that arrangement the turns of the coil are preferably at a uniform spacing from each other, like also the turns of a corkscrew. In addition the free end of the fixing element is preferably sharpened to a point.
The first fixing means is preferably fixed with its distal end to the electrode line so that the free end of the first fixing means is closer to the proximal end of the electrode line. In conjunction with a second fixing element which is coiled in a corkscrew-like fashion, with an opposite direction of rotation, at the distal end of the electrode line, it is possible, as described hereinafter, to avoid loading the electrode line when the myocardium contracts.
In another embodiment, the first fixing element has a second free end which with respect to the electrode line involves the same tangential orientation as the first free end, but an opposite axial orientation, with the first fixing element fixed to the electrode line between both free ends. This central fixing of the first fixing element to the electrode line with two free ends has the advantage, by virtue of the oppositely directed directions of rotation of the two resulting helix portions, that, when the helix portions are screwed into adjacent tissue, a certain stressing of the two free ends relative to each other occurs. That stressing effect results in secure fixing of the securing action which otherwise can rather be released by unintentional rotational movements.
In most embodiments, the electrode element carries a second fixing element at its distal end. Such an electrode arrangement can be actively fixed to the body tissue at two locations, more specifically at its distal end and at a spacing therefrom, so that the two fixing elements also assume a fixed position relative to each other, with respect to the body tissue.
In that arrangement the second fixing element is also of a corkscrew-like configuration in the form of a helical coil with a free end, wherein the second fixing element involves a direction of rotation opposite to the first fixing element. Even if the second fixing element is rigidly connected to the electrode line, the electrode line can be rotated from its proximal end about the longitudinal axis thereof in order in that way to cause both fixing elements to penetrate into adjacent body tissue in the same direction. As a consequence of the opposite directions of rotation of the two fixing elements and the measure, which is directly related thereto, of fixing the first fixing element with its distal end to the electrode line, the myocardium is upset between the two fixing elements when they are screwed in. This avoids high levels of loading on the electrode line in the event of contraction of the myocardium.
Instead of the second fixing element being rigidly connected to the electrode line in such a way that the second fixing element, like the first fixing element, also rotates with the electrode line, it is also possible to provide a drive for the second fixing element, which makes it possible for the second fixing element to be driven with a rotational movement about the longitudinal axis of the electrode line, independently of the electrode line, more particularly preferably from the proximal end of the electrode line. Preferably the first fixing element is connected to the electrode line while the second fixing element is rotatable with respect to the electrode line by means of a bar which is introduced in the electrode line. That kind of drive is known per se for actively fixable screw electrodes at the distal end of the electrode line.
In one embodiment, the electrode arrangement is one which has a first electrode with an electrically conductive surface on the surface of the electrode line, which is adjacent to the free end of the first fixing element. This arrangement of the first electrode relative to the first fixing element ensures intensive contact of the first electrode with the body tissue in the long term. In that case the first fixing element is preferably electrically conductively connected to the first electrode and in that way itself becomes a component part of the first electrode. The first electrode moreover is usually formed by the surface of the electrode line, around which the first fixing element passes.
In most embodiments, the electrode arrangement has at least one second electrode at its distal end. A second electrode of that kind, in particular in the immediate proximity of the second fixing element which is usually part of the second electrode, permits the delivery of bipolar and in particular bi-phase stimulation pulses to the body tissue. In that respect, the bi-phase stimulation pulses can overlap in respect of time.
One particular embodiment of an electrode arrangement includes precisely two fixing elements which are in the form of corkscrew-like helical coils, which are each provided with a free end adapted to penetrate into tissue and which are arranged on the one hand at the distal end of the electrode line and on the other hand remote therefrom, and at least two electrodes with an electrically conductive surface, which are respectively arranged in the immediate proximity of the fixing means. An electrode arrangement of that kind advantageously permits bi-phase stimulation of the high septum of a heart.
Such an embodiment of an electrode line further includes two coaxial, electrically conductive coils which are electrically insulated relative to each other and with respect to the exterior of the electrode line and of which the outer coil contacts the first electrode which is remote from the distal end of the electrode line while the inner coil contacts the electrode at the distal end of the electrode line. An electrode line of that kind has a high level of flexibility without the danger of the electrically conductive coils breaking. In addition an electrode line of that kind represents secure contacting of the electrodes.
Most embodiments of the electrode line will also have control means with which the distal end can be deflected in the bilateral direction in per se known manner. That permits the targeted guidance of the electrode line to its target location. Control means of that kind are known for example from U.S. Pat. Nos. 5,254,088, 5,364,351, 5,376,109 and 5,423,884, as well as European published application 0 667 126 and German application 35 07 119.